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RESOLVER(3)                Linux Programmer's Manual               RESOLVER(3)

       res_init, res_query, res_search, res_querydomain, res_mkquery,
       res_send, dn_comp, dn_expand - resolver routines

       #include <netinet/in.h>
       #include <arpa/nameser.h>
       #include <resolv.h>
       extern struct state _res;

       int res_init(void);

       int res_query(const char *dname, int class, int type,
              unsigned char *answer, int anslen);

       int res_search(const char *dname, int class, int type,
              unsigned char *answer, int anslen);

       int res_querydomain(const char *name, const char *domain,
              int class, int type, unsigned char *answer,
              int anslen);

       int res_mkquery(int op, const char *dname, int class,
              int type, char *data, int datalen, struct rrec *newrr,
              char *buf, int buflen);

       int res_send(const char *msg, int msglen, char *answer,
              int anslen);

       int dn_comp(unsigned char *exp_dn, unsigned char *comp_dn,
              int length, unsigned char **dnptrs, unsigned char *exp_dn,
              unsigned char **lastdnptr);

       int dn_expand(unsigned char *msg, unsigned char *eomorig,
              unsigned char *comp_dn, unsigned char *exp_dn,
              int length);

       These functions make queries to and interpret the responses from
       Internet domain name servers.

       The res_init() function reads the configuration files (see resolv+(8))
       to get the default domain name, search order and name server
       address(es).  If no server is given, the local host is tried.  If no
       domain is given, that associated with the local host is used.  It can
       be overridden with the environment variable LOCALDOMAIN.  res_init() is
       normally executed by the first call to one of the other functions.

       The res_query() function queries the name server for the fully-
       qualified domain name name of specified type and class.  The reply is
       left in the buffer answer of length anslen supplied by the caller.

       The res_search() function makes a query and waits for the response like
       res_query(), but in addition implements the default and search rules
       controlled by RES_DEFNAMES and RES_DNSRCH (see description of _res
       options below).

       The res_querydomain() function makes a query using res_query() on the
       concatenation of name and domain.

       The following functions are lower-level routines used by res_query().

       The res_mkquery() function constructs a query message in buf of length
       buflen for the domain name dname.  The query type op is usually QUERY,
       but can be any of the types defined in _arpa/nameser.h_.  newrr is
       currently unused.

       The res_send() function sends a pre-formatted query given in msg of
       length msglen and returns the answer in answer which is of length
       anslen.  It will call res_init(), if it has not already been called.

       The dn_comp() function compresses the domain name exp_dn and stores it
       in the buffer comp_dn of length length.  The compression uses an array
       of pointers dnptrs to previously compressed names in the current
       message.  The first pointer points to the beginning of the message and
       the list ends with NULL.  The limit of the array is specified by
       lastdnptr.  if dnptr is NULL, domain names are not compressed.  If
       lastdnptr is NULL, the list of labels is not updated.

       The dn_expand() function expands the compressed domain name comp_dn to
       a full domain name, which is placed in the buffer exp_dn of size
       length.  The compressed name is contained in a query or reply message,
       and msg points to the beginning of the message.

       The resolver routines use global configuration and state information
       contained in the structure _res, which is defined in _resolv.h_.  The
       only field that is normally manipulated by the user is _res.options.
       This field can contain the bitwise ``or'' of the following options:

              True if res_init() has been called.

              Print debugging messages.

              Accept authoritative answers only.  res_send() continues until
              it fins an authoritative answer or returns an error.  [Not
              currently implemented].

              Use TCP connections for queries rather than UDP datagrams.

              Query primary domain name server only.

              Ignore truncation errors.  Don't retry with TCP.  [Not currently

              Set the recursion desired bit in queries.  Recursion is carried
              out by the domain name server, not by res_send().  [Enabled by

              If set, res_search() will append the default domain name to
              single component names, ie. those that do not contain a dot.
              [Enabled by default].

              Used with RES_USEVC to keep the TCP connection open between

              If set, res_search() will search for host names in the current
              domain and in parent domains.  This option is used by
              gethostbyname(3).  [Enabled by default].

       The res_init() function returns 0 on success, or -1 if an error occurs.

       The res_query(), res_search(), res_querydomain(), res_mkquery() and
       res_send() functions return the length of the response, or -1 if an
       error occurs.

       The dn_comp() and dn_expand() functions return the length of the
       compressed name, or -1 if an error occurs.

       /etc/resolv.conf          resolver configuration file
       /etc/host.conf            resolver configuration file

       BSD 4.3

       gethostbyname(3), hostname(7), named(8), resolv+(8)

BSD                               1993-05-21                       RESOLVER(3)


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